The present invention relates to a thickness detecting apparatus for detecting a thickness of a sheet or the like.
Conventionally, as a system for measuring a thickness of medium in order to determine whether foreign object sticks to a sheet or the like, there has been proposed such a system that a banknote is held between a stationary roller and a displaceable roller so as to detect a displacement of the displaceable roller (Refer to JP-U-6-61850).
Explanation will be made of the above-mentioned system with reference to FIG. 9 which is a partly sectioned front view. As shown, a banknote 120 is held between a displaceable roller 110 and a stationary roller 130, and a sensor 101 is arranged above the displaceable roller 110.
The displaceable roller 110 is composed of a cylindrical sheath roller 111 and a core shaft 113 and an elastic body 112 made of rubber or the like and interposed between both roller 110 and core shaft 113. The stationary roller 130 is composed of a roller 132 and a core shaft 131 inserted in the roller 132.
With this configuration, the displaceable roller is pressed against the stationary roller 130 by means of the elastic body 122 by a pressing force having a force center, uniformly thereover in the longitudinal direction of the roller 130.
The displaceable roller 110 and the stationary roller 130 are arranged in a plurality of pairs which are laid discretely in a direction widthwise of a transfer path 140 as shown in FIG. 10A which is a plan view and FIG. 10B which is a side view in order to cover the entire zone of the transfer path.
Since the width of the banknote 120 is smaller than the width of the transfer path 140, in particular, there would be caused such a case that the banknote 120 overlaps with the roller 110 only by a length which is not longer than about a half of the length of the roller as shown in FIG. 10A the displaceable roller 110 at a side end side. That is, the roller with which the banknote 120 overlaps by not longer than a half of the length thereof, would be slanted.
Meanwhile, a single sensor 110 is arranged right above of the center of one of the displaceable rollers 110 as shown in FIG. 11A which is a front view. In this case, should foreign matter 150 such as a tape sticking to the banknote 120 passes by an end part of the displaceable roller 110, only a half of a height of the foreign matter could be detected at the center of the displaceable roller 110, resulting in a problem of difficulty in detecting the foreign matter.
Thus, these days, a pair of sensors 110 are arranged respectively at opposite ends of the displaceable roller 110 as shown in FIG. 11B which is a front view, in order to improve the detection.
However, in this configuration, if the banknote 120 overlaps with the displaceable roller 110 by only a half of the length of the roller 110, as shown in FIGS. 10A and 10B, the displaceable roller 110 slants largely as a sew-saw like-manner, and resulting in a one-side lift-up condition as shown in FIG. 12A which is a front view.
Thus, the thickness of the banknote 120 would be detected by a value which is relatively larger than its actual thickness, resulting in erroneous detection of foreign matter although no foreign matter is present. Further, should setting be made such that this situation is set so as to prevent erroneous detection of foreign matter, there would be caused problems of impossible detection of foreign matter 150 having a thickness smaller than the above-mentioned one-side lift-up and of impossible detection of concave and convex features of a banknote having a thickness which is smaller than the one-side lift-up, as shown in FIG. 12B which is a front view.
Thus, in order to prevent the above-mentioned erroneous detection, data relating to a thickness of an end part of a banknote should have been discarded.
Further, in order to prevent occurrence of a one-side lift-up situation, as shown in FIG. 13 which is a plan view, it had to be better to arrange the displaceable roller 110 at a position where the medium does not overlaps by a half, but in this case, the displaceable roller 110 should be located only at the center of the transfer path, there has be caused a problem of further decreasing a possible detection area.
Meanwhile, as an another method for restraining affection by a one side lift-up, there may be considered such a method in which the width of the displaceable roller 110 is narrowed in order to reduce the volume of data which should be discarded. However, this configuration would cause the number of rollers to increase, there has been caused a problem of increasing the costs.